Pressure regulator for maintaining a stable flow level of a fluid

ABSTRACT

A flow regulator for maintaining a stable rate of flow of a fluid in a flow channel (2), comprising a flow-actuating element (4) which is movable under the influence of a pressure drop in the fluid flow, and a throttle valve (10) for regulating the fluid flow under the influence of said element (4). The fluid-actuated element (4) constitutes a control element for a servo means (11) comprising a pilot valve (17) for controlling the movement of a drive means (12) coupled to a valve body (19) in the throttle valve (10), and which, by means of the servo means (11), is arranged to be moved in a smooth manner independently of sudden changes in the fluid flow. The control element is influenced by a prestressed spring (9) acting in the opposite direction to the flow direction, so that the control element (4) is moved in the flow direction only when the rate of flow exceeds a preselected level.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a flow regulator for maintaining a stable rateof flow of a fluid in a flow channel, comprising a flow-actuated elementwhich is movable under the influence of a pressure drop in the fluidflow, and a throttle valve for regulating the fluid flow under theinfluence of said element.

A typical field of use for such a regulator is in connection withhydraulic pumps for unloading cargo tanks for oil or the like on e.g. atanker, wherein the pumps are connected to and driven from a ringconduit transporting hydraulic liquid under a very high pressure, morespecifically about 300 bars (30 000 kPa). Such applications utilizepumps of very large power, on the order of megawatts. In front of eachpump a flow regulator is used for ensuring a stable liquid supply forthe operation of the pumps in order to prevent them from "running riot"when they are about to empty the reservoir and start sucking air. Such asituation with overspeed of the pump will result in damage thereof inthe course of a very short time.

Different types of regulators have been developed for this purpose. Suchregulators operate to restrict or throttle the supply of hydraulicliquid as soon as changes occur in the operating conditions which mayhave a tendency to increase the liquid supply in the flow channel to thepump motor. The known types of flow regulators are, however, encumberedwith problems in that they are complicated and in that they absorb aconsiderable amount of energy under normal operating conditions (i.e.with a little throttling of the liquid flow). This is a consequence ofthe fact that a considerable pressure drop has to be established acrossthese known regulators in order to produce the forces used forstabilizing the through-put. With a conduit pressure of about 300 bars,it may for example be the question of a pressure drop of about 10 barsfor each regulator. This in reality involves an energy loss of the orderof 30 kW, which results in a substantial heating of the oil; somethingwhich in turn requires artificial cooling. It is obvious that this iseconomically unfavorable and also renders as the system structure morecomplicated.

Thus, it is an object of the invention to provide a flow regulator whichis able to operate with a substantially reduced pressure drop in theflow channel in relation to the known regulators.

A further object is to provide such a flow regulator giving a moresensitive regulation with a short response time and a smoother responsethan what is achieved with the regulators according to the prior art.

The above-mentioned objects are achieved with a flow regulator of theintroductorily stated type which, according to the invention, ischaracterized in that the flow-actuated element constitutes a controlelement for a servo means comprising a pilot valve for controlling themovement of a drive means coupled to a valve body in the throttle valve,and which, by means of the servo means, is arranged to be moved in asmooth manner independently of sudden changes in the fluid flow, thecontrol element being arranged to be moved in the flow direction onlywhen the rate of flow exceeds a preselected level.

In the flow regulator according to the invention, the flow-actuatedelement operates as a control element in a servo control of the throttlevalve. By means of this technique there is achieved an efficientstabilization of the fluid flow with a very moderate pressure dropacross the regulator. It is estimated that the pressure drop may bereduced to approximately 1 bar; i.e. to 1/10 of the pressure droprequired in the regulators according to the prior art. The servo controlabsorbs some energy, but this is quite inconsequential compared to theenergy lost in the existing solutions.

The flow regulator according to the invention distinguishes itself inthat it has a small energy demand under normal operating conditions, andin that it maintains a stable flow level even if sudden changes in theoperating conditions occur. By, inter alia, designing the throttle valvesuch that an efficient balancing of the pressure influencing the valvebody in the throttle valve is obtained, the flow control functions wellwith a very moderate use of servo. Thus, by means of the utilizedtechnique, a very "smooth" and precise flow regulation has beenachieved, even with a fluid pressure of up to 300 bars.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described below in connection with anexemplary embodiment with reference to the drawings, wherein

FIG. 1 shows a longitudinally sectioned view of a flow regulatoraccording to the invention; and

FIGS. 2 and 3 show enlarged sectional views of the servo means with thepilot valve in FIG. 1 in two different operational positions.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, the flow regulator according to the invention will bedescribed in connection with the regulation of a liquid flow, but it isemphasized that the solution is suitable for any fluid.

As appears from FIG. 1, the shown embodiment of the flow regulatorcomprises a body 1 containing a flow channel 2 and in which theregulator elements are built in as shown next to the flow channel. Inthe flow channel 2, there is provided a pressure-drop producing means inthe form of an orifice 3 for the generation of a flow-dependent forcefor actuating or influencing the flow-actuated element of the regulator.In the illustrated embodiment, this element is a piston 4 which ismovable in a cylindrical cavity which is divided by the piston into afirst chamber 5 and a second chamber 6. The first chamber 5 is connectedto the channel 2 through a port 7 upstream of the orifice 3, and thesecond chamber 6 is connected to the channel 2 through a port 8downstream of the orifice 3. Thus, the pressure in the chamber 6 isreduced in relation to the pressure in the chamber 5 with a valuecorresponding to the pressure drop which is generated across the orifice3 and which in turn is dependent on the rate of flow (the flow level) inthe channel 2. Thus, the piston 4 is influenced by a force seeking tomove the piston in the flow direction. However, the piston 4 is alsoinfluenced by a suitably prestressed spring 9 counteracting thefirst-mentioned force on the piston 4, so that the liquid flow has toexceed a certain level before the piston 4 is moved in the flowdirection. The arrangement in connection with the spring 9 will befurther described later.

The regulator comprises a throttle valve 10 for regulating the liquidflow in the channel 2 under the influence of the piston 4, the pistonconstituting a control element for a servo means 11 for controllingmovement of a drive means 12 for operating the throttle valve.

As shown in FIG. 1, the drive means 12 is arranged in the second chamber6 and comprises a piston housing 13 which is fixedly mounted in the body1, and a drive piston 14 which, together with the piston housing,defines a third chamber 15 on the side of the piston 14 facing away fromthe throttle valve 10. The piston housing 13 is formed from a cup-shapedbody which is outwardly open on the side of the drive piston 14 facingthe throttle valve 10, so that the piston at this side is influenced bythe pressure in the second chamber 6. On its opposite side the piston 14is influenced by the force from a suitably prestressed drive spring 16and by the pressure from liquid which has been supplied to the thirdchamber 15 by means of the pilot valve 17 of the servo means 11. Thepiston 14 is fixedly connected through a piston rod 18 to a valve body19 in the throttle valve 10.

The pilot valve 17 of the servo means 11 comprises a center shaft 20arranged on the control element piston 4 and consisting of a pair ofmembers 21, 22 extending at opposite sides of the piston, and a guidingsleeve 23 arranged for the center shaft 20 which is connected to thedrive piston 14 and extends outside of the third chamber 15 towards thepiston 4. The center shaft 20 on its surface is provided with a numberof longitudinally extending channels 24 which, at one end, communicatewith the second chamber 6 through first ports 25 through the wall of theguiding sleeve 23, and which, at their other end, can be brought intocommunication with the third chamber 15 through second ports 26 in thewall of the guiding sleeve. Further, the center shaft 20 comprises atransverse passage 27 which can be brought into communication with thesecond ports 26 of the guiding sleeve 23 when these are shut off fromthe channels 24, and which communicates with a passage 28 extendingthrough the center shaft 20 in the longitudinal direction thereof andcommunicates with an outlet 29 for the escape of liquid from the thirdchamber 15. This outlet may open into the external ambient pressure of 1atmosphere.

The longitudinal passage 28 of the center shaft 20 extends as shownthroughout the center shaft and opens at opposite ends thereof, so thatit is pressure-balanced in the axial direction.

The control function of the pilot valve consists in that it controlsliquid to or from the third chamber 15 in such a manner that the drivepiston 14 at any time is forced to follow the movement of the controlelement piston 4 and therewith the movement of the center shaft 20. Aswill be understood, the drive piston 14 is moved in one or the otherdirection when the resulting force from the drive spring 16 and theliquid pressure in the third chamber 15 exceeds or becomes less than theforce influence on the piston because of the pressure in the secondchamber 6.

By the servo means one achieves that the drive piston 14 is moved in asmooth manner even if a sudden pressure change occurs in the liquid flowin the channel 2, consequently a sudden movement of the flow-actuatedpiston 4 will result in movement of the drive piston 14 only when thechamber 15 is filled or emptied sufficiently for achieving the necessarydifferential pressure across the piston 14.

The operating principle of the pilot valve is further in FIGS. 2 and 3wherein the shown arrows indicate the liquid flow in the servomechanism. FIG. 2 shows the liquid flow when the piston 4 and the centershaft 20 are moved downwards and the chamber 15 is filled with liquid sothat the drive piston 14 is moved correspondingly downwards, and FIG. 3shows the liquid flow when the piston 4 is moved upwards and the chamber15 is emptied of liquid so that the drive piston 14 is movedcorrespondingly upwards.

As shown in FIG. 1, the upper part 22 of the center shaft 20 at theoutlet 29 is introduced into a cavity 30 in a closing body 31 which in amanner not further shown, is adjustable in the longitudinal direction ofthe center shaft in the body 1. The cavity 30 has an outlet opening 32which is directed towards the piston 4 and is defined by a collar 33which is arranged to cooperate with an annular seat 34 around the centershaft. The outlet 29 thereby may be closed in connection withshutting-off of the throttle valve 10, as described below.

The above-mentioned prestressing spring 9 for preadjustment of the flowlevel through the regulator is, as shown, restrained between the outletend of the closing body 31 and a support member 35 at the end of thecenter shaft 20, so that the prestressing force of the spring 9 isreduced by movement of the closing body 31 in the direction towards theseat 34.

The throttle valve 10 of the regulator comprises a housing 36 having acylindrical cavity 37 wherein the valve body 19 is slidably arranged ina sealing manner. In the shown embodiment, a sealing ring 38 is arrangedbetween the valve body 19 and the adjacent housing wall. However, thissealing ring may be omitted with an accurate adaptation and polishing ofthe sliding surfaces. The cavity 37 merges into the outlet opening 39 ofthe regulator, the downstream end of the cavity communicating with theflow channel 2 through a number of radial ports 40 symmetricallyarranged in the peripheral wall of the housing 36, and through anannular space 41 arranged in the body 1 around the housing 36.

As shown, the valve body 19 is provided with through-going axialchannels 42 for equalizing the pressure difference between the endsurfaces of the valve body. By the axial movement of the valve bodythere is obtained a stepless and not very force-demanding change of theeffective flow cross-section through the radially arranged ports 40.When the flow regulator is completely closed, the lower edge of thevalve body 19 is pressed against a seat 43 in the valve housing 36. Thisseat is disposed at a certain distance from the ports 40 for minimizingpressure effects when the valve body 19 causes a considerable throttlingof the liquid flow.

The through-put of the regulator may be adjusted to a desired level byestablishing a given prestressing of the spring 9. The prestressing ofthe spring is dependent on the position of the closing body 31 which inthis context may also be designated "control cylinder". This may bepositioned by manual or pneumatic control according to known technique.In FIG. 1, the control cylinder is raised to its uppermost positionwhereby the regulator is adjusted to maximum through-put. Further, itmay be assumed that the liquid flow through the system corresponds tothe set level. The force trying to press the piston 4 downwards, then isequal to and oppositely directed in relation to the tension of thespring. In this situation the throttle valve body 19 is maintained in aposition allowing full through-put or through-flow via the ports 40 ofthe throttle valve 10.

If the external conditions change and the liquid flow starts increasing,the piston 4 immediately will be pressed downwards and quickly see to itthat the throttle valve 10 enters into operation and thereby maintainsthe flow level. An important property of the illustrated embodiment isthat the piston 4 is not influenced by forces which may createinstability in the liquid regulation. Thus, importance is attached tobalancing undesired pressure effects on the center shaft. All portstherefore are symmetrically placed and, as mentioned, the throughpassage of the center shaft provides for eliminating undesired axialforces.

When the control cylinder 31 is positioned in its lowermost position,the collar 33 rests sealingly against the seat 34, so that the outlet 29is closed. In this situation liquid can not be discharged from thechamber 15, and this is filled gradually with liquid until the spring 16has pressed the throttle valve body 19 downwards against the seat 43, sothat the throttle valve is closed.

In the illustrated embodiment, the valve body 19 is disposed at theinside of the ports 40 in the valve housing 36. In an alternativeembodiment (not shown) the valve body may be disposed at the outside ofthe ports, but this would entail an undesired dimensional increase ofthe movable parts. It is also conceivable to place the flow-actuatedpiston 4 in the liquid flow in the flow channel, and thereby avoid thespecial pressure-drop generating means 3. It has been found, however,that this gives a somewhat poorer stability.

I claim:
 1. A flow regulator for maintaining a stable rate of flow of afluid in a flow channel (2), comprising a flow-actuated element (4)which is movable under the influence of a pressure drop in the fluidflow, and a throttle valve (10) for regulating the fluid flow under theinfluence of said element (4), characterized in that flow-actuatedelement (4) constitutes a control element for a servo means (11)comprising a pilot valve (17) for controlling the movement of a drivemeans (12) coupled to a valve body (19) in the throttle valve (10) andwhich, by means of the servo means (11), is arranged to be moved in asmooth manner independently of sudden changes in the fluid flow, saidcontrol element (4) being arranged to be moved in the flow directiononly when the rate of flow exceeds a preselected level and beinginfluenced by a prestressed spring (9) acting in the opposite directionto the flow direction, the prestressing force is adjustable for settingof the preselected flow level, said control element (4) including apiston forming a partition between a first chamber (5) connected to theflow channel (2) upstream of a pressure-drop orifice (3) in the channel,and a second chamber (6) connected to the channel (2) at the downstreamside of the orifice (3), and that the drive means (12) is arranged inthe second chamber (6) and comprises a piston housing (3) and a drivepiston (14) which together defines a third chamber (15) at the side ofthe piston (14) facing away from the throttle valve (10), the thirdchamber (15) by means of the pilot valve (17) being arranged to befilled with fluid from the second chamber (6) or emptied of fluid independence on the movement of the control element (4), the drive piston(14) at the side facing the throttle valve (10) being influenced by thepressure in the second chamber (6), and on the opposite side beinginfluenced by the force from a prestressed drive spring (16) and by thepressure from the fluid supplied to the third chamber (15), so that thedrive piston (14) is moved when the resulting force from the drivespring (16) and the fluid pressure in the third chamber (15) exceeds orbecomes less than the force influence from the pressure in the secondchamber (6).
 2. A flow regulator according to claim 1, characterized inthat the pilot valve (17) comprises a center shaft (20) arranged on thecontrol element piston (4) and a guiding sleeve (23) arranged for thecenter shaft and which is connected to the drive piston (14) and extendsoutside the third chamber (15), the center shaft (20) on its surfacebeing provided with a number of longitudinally extending channels (24)which, at one end, communicate with the second chamber (6) through firstports (25) through the wall of the guiding sleeve (23), and which attheir other end can be brought into communication with the third chamber(15) through second ports (26) in the wall of the guiding sleeve (23),and the center shaft (20) further comprising a transverse passage (27)which can be brought into communication with the second ports (26) ofthe guiding sleeve (23) when these are shut off from the channels (24),and which communicates with a passage (28) extending through the centershaft (20) in the longitudinal direction thereof and communicating withan outlet (29) for escape of fluid from the third chamber (15).
 3. Aflow regulator according to claim 2, characterized in that thelongitudinally extending passage (28) of the center shaft (20) extendsthroughout the center shaft (20) and opens at opposite ends thereof, sothat the shaft is pressure-balanced in the axial direction.
 4. A flowregulator according to claim 2, characterized in that the end of thecenter shaft (20) at said outlet (29) is inserted into a cavity (30) ina closing body (31) which is adjustable in the longitudinal direction ofthe center shaft (20), the cavity (30) having an outlet opening (32)which is directed towards the control element piston (4) and is arrangedto cooperate with a seat (34) in order to close the outlet (29) to causeclosing of the throttle valve (10).
 5. A flow regulator according toclaim 4, characterized in that the prestressing spring (9) isconstrained between the outlet end of the closing body (31) and asupport member (35) at the end of the center shaft (20), so that theprestressing force of the spring (9) is reduced with movement of theclosing body (31) in the direction towards said seat (34).
 6. A flowregulator according to claim 5 CHARACTERIZED IN that the drive piston(14) of the drive means (12) through a piston rod (18) is directlyconnected to the valve body (19) of the throttle valve (10).
 7. A flowregulator according to claim 6, CHARACTERIZED IN that the throttle valve(10) comprises a housing (39) having a cylindrical cavity (37) whereinthe valve body (19) is slidably arranged and which merges into theoutlet opening (39) of the regulator, the downstream end of the cavity(37) communicating with said flow channel (2) through a number of radialports (40) which are symmetrically arranged in the peripheral wall ofthe housing (36).
 8. A flow regulator according to claim 7,CHARACTERIZED IN that the valve body (19) of the throttle valve (10) isprovided with through-going axial channels (42) for equalizing thepressure difference between the end surfaces of the valve body (19). 9.A flow regulator for maintaining a stable rate of flow of a fluid in aflow channel (2), comprising a flow-actuated element (4) which ismovable under the influence of a pressure drop in the fluid flow, and athrottle valve (10) for regulating the fluid flow under the influence ofsaid element (4), characterized in that flow-actuated element (4)constitutes a control element for a servo means (11) comprising a pilotvalve (17) for controlling the movement of a drive means (12) coupled toa valve body (19) in the throttle valve (10), and which, by means of theservo means (11), is arranged to be moved in a smooth mannerindependently of sudden changes in the fluid flow, said control element(4) being arranged to be moved in the flow direction only when the rateof flow exceeds a preselected level, said control element (4) includinga piston forming a partition between a first chamber (5) connected tothe flow channel (2) upstream of a pressure-drop orifice (3) in thechannel, and a second chamber (6) connected to the channel (2) at thedownstream side of the orifice (3), and that the drive means (12) isarranged in the second chamber (6) and comprises a piston housing (3)and a drive piston (14) which together defines a third chamber (15) atthe side of the piston (14) facing away from the throttle valve (10),the third chamber (15) by means of the pilot valve (17) being arrangedto be filled with fluid from the second chamber (6) or emptied of fluidin dependence on the movement of the control element (4), the drivepiston (14) at the side facing the throttle valve (10) being influencedby the pressure in the second chamber (6), and on the opposite sidebeing influenced by the force from a prestressed drive spring (16) andby the pressure from the fluid supplied to the third chamber (15), sothat the drive piston (14) is moved when the resulting force from thedrive spring (16) and the fluid pressure in the third chamber (15)exceeds or becomes less than the force influence from the pressure inthe second chamber (6).
 10. A flow regulator according to claim 9,characterized in that the pilot valve (17) comprises a center shaft (20)arranged on the control element piston (4) and a guiding sleeve (23)arranged for the center shaft and which is connected to the drive piston(14) and extends outside the third chamber (15), the center shaft (20)on its surface being provided with a number of longitudinally extendingchannels (24) which, at one end, communicate with the second chamber (6)through first ports (25) through the wall of the guiding sleeve (23),and which at their other end can be brought into connection with thethird chamber (15) through second ports (26) in the wall of the guidingsleeve (23), and the center shaft (20) further comprising a transversepassage (27) which can be brought into connection with the second ports(26) of the guiding sleeve (23) when these are shut off from thechannels (24), and which communicates with a passage (28) extendingthrough the center shaft (20) in the longitudinal direction thereof andcommunicating with an outlet (29) for escape of fluid from the thirdchamber (15).
 11. A flow regulator according to claim 10, characterizedin that the longitudinally extending passage (28) of the center shaft(20) extends throughout the center shaft (20) and opens at opposite endsthereof, so that the shaft is pressure-balanced in the axial direction.12. A flow regulator according to claim 10, characterized in that theend of the center shaft (20) at said outlet (29) is inserted into acavity (30) in a closing body (31) which is adjustable in thelongitudinal direction of the center shaft (20), the cavity (30) havingan outlet opening (32) which is directed towards the control elementpiston (4) and is arranged to cooperate with a seat (34) in order toclose the outlet (29) to cause closing of the throttle valve (10).
 13. Aflow regulator according to claim 4, characterized in that theprestressing spring (9) is constrained between the outlet end of theclosing body (31) and a support member (35) at the end of the centershaft (20), so that the prestressing force of the spring (9) is reducedwith movement of the closing body (31) in the direction towards saidseat (34).
 14. A flow regulator according to claim 9, characterized inthat the throttle valve (10) comprises a housing (39) having acylindrical cavity (37) wherein the valve body (19) is slidably arrangedand which merges into the outlet opening (39) of the regulator, thedownstream end of the cavity (37) communicating with said flow channel(2) through a number of radial ports (40) which are symmetricallyarranged in the peripheral wall of the housing (36).
 15. A flowregulator according to claim 2, characterized in that the throttle valve(10) comprises a housing (39) having a cylindrical cavity (37) whereinthe valve body (19) is slidably arranged and which merges into theoutlet opening (39) of the regulator, the downstream end of the cavity(37) communicating with said flow channel (2) through a number of radialports (40) which are symmetrically arranged in the peripheral wall ofthe housing (36).
 16. A flow regulator according to claim 1,characterized in that the valve body (19) of the throttle valve (10) isprovided with through-going axial channels (42) for equalizing thepressure difference between the end surfaces of the valve body (19). 17.A flow regulator according to claim 9, characterized in that the valvebody (19) of the throttle valve (10) is provided with through-goingaxial channels (42) for equalizing the pressure difference between theend surfaces of the valve body (19).
 18. A flow regulator according toclaim 1, characterized in that the throttle valve (10) comprises ahousing (39) having a cylindrical cavity (37) wherein the valve body(19) is slidably arranged and which merges into the outlet opening (39)of the regulator, the downstream end of the cavity (37) communicatingwith said flow channel (2) through a number of radial ports (40) whichare symmetrically arranged in the peripheral wall of the housing (36).19. A flow regulator for maintaining a smooth and stable rate of flow ofa liquid in a flow channel under a relatively high pressure, e.g.100-300 bars, comprisinga flow actuated element (4) which is moveableunder the influence of a pressure drop in the liquid flow, and which isinfluenced by a preset force acting oppositely to the flow direction, sothat the element is only moved when the rate of flow exceeds apreselected level, a pressure-balanced throttle valve (10) having avalve body (19) for regulating the liquid flow under the influence ofthe flow-actuated element (4), and a servo means (11) which is connectedbetween the flow-actuated element (4) and the throttle valve (19), saidelement constituting a control element for the servo means, the servomeans (11) comprising a pressure-balanced pilot valve (17) arranged tocooperate with a drive means (13, 14, 18) in such a manner that thedrive means after a time delay follows the movement of the controlelement without exertion of any counter-acting force on the controlelement, the drive means being rigidly connected to the valve body (19)of the throttle valve (10) to slave-control the valve body so that themovement thereof after said time delay corresponds to the movement ofthe flow-actuated element.
 20. A flow regulator according to claim 1,wherein said control element (4) is influenced by a prestressed springproviding said preset force on the control element.